Methods For Measuring Roll, Pitch and Yam Angle and Orientation Misalignment in Objects

ABSTRACT

A method for determining angular orientation of an object in two or more directions. The method includes: generating a scanning polarized RF source signal; receiving the scanning polarized RF source signal at one or more cavities of a sensor disposed on the object; measuring the scanning polarized RF source signal at a first portion of the sensor; reflecting the scanning polarized RF source signal toward a second portion of the sensor; measuring the scanning polarized RF source signal at the second portion of the sensor; and determining the angular orientation of the object in the two or more directions based on the measured signal at the first and second portions of the sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 15/986,765, filed on May 22, 2018, now U.S. Pat.No. 10,948,293 issued on Mar. 16, 2021, which claims benefit to earlierfiled U.S. Provisional Patent Application No. 62/510,232, filed on May23, 2017, the entire contents of each of which are incorporated hereinby reference.

GOVERNMENT RIGHTS

This invention was made with Government support under contractsW15QKN-12-C-0036 and W15QKN-17-C-0004 awarded by the United States Army.The Government has certain rights in the invention.

BACKGROUND 1. Field

The present disclosure relates generally to angular orientation sensorsand, more particularly, to systems and methods for the design of cavitysensors for measuring roll, pitch and yaw angles using polarized RadioFrequency (RF) signals from scanning polarized RF reference sources andmethods and systems for configuring the cavity sensors to function as“homing” sensors for guiding an object remotely to a desired location.

2. Prior Art

For guidance and/or steering purposes, all manned and unmanned mobileplatforms, such as land vehicles, powered or non-powered airborneplatforms, surface or submerged marine platforms, or various spacevehicles, require onboard information as to their absolute (relative toearth) position and orientation (sometimes called attitude) or theirposition and orientation relative to another object such as a referenceplatform or a target object.

This position and orientation information is particularly important forunmanned and guided platforms such as mobile robots, Unmanned AerialVehicles (UAV), unmanned guided surface or submerged platforms, and thelike. This is also the case in future smart and guided projectiles,including gun-fired munitions, mortars and missiles. Such platforms willalso require the aforementioned absolute and/or relative position andorientation information onboard the platform for closing the feedbackguidance and control loop to guide the platform to the desired target ortrack a specified trajectory or the like.

In certain cases, the onboard position and orientation information(absolute or relative to the target, a reference station, another mobileplatform, etc.) can be provided by an outside source, for example, byGPS for position or by a radar reading or optical signal that isreflected off some target or received by the mobile platform. In othercases, it is either required or is highly desirable to have autonomoussensors on board the mobile platform, including gun-fired projectiles,mortars and missiles, to directly measure the position and orientationof the object with respect to a fixed object (for example a groundstation) or a moving object (for example a moving target).

It is noted that even though in this disclosure all references are madeto moving platforms, it IS appreciated by those of ordinary skill in theart that the provided description also includes the measurement of theposition and orientation of one object relative to another object, oneor both of which may be fixed to a third object such as the ground.

Currently available sensors for remote measurement of the angularposition (attitude) of an object relative to the earth or another object(target or weapon platform) can be divided into the following five majorclasses.

The first class of sensors measure changes in the angular position usinginertial devices such as accelerometers and gyros. Inertial basedangular orientation sensors, however, generally suffer from drift andnoise error accumulation problems. In such sensors, the drift and themeasurement errors are accumulated over time since the acceleration mustbe integrated twice to determine the angular position. Thus, the errorin the angular position measurement increases over time. In addition,the initial angular orientation and angular velocity of the object mustbe known accurately. Another shortcoming of inertia based angularposition sensors is that the angular position of one object relative toanother cannot be measured directly, i.e., the orientation of eachobject relative to the inertia frame must be measured separately andused to determine their relative angular orientation. As a result,errors in both measurements are included in the relative angularorientation measurement, thereby increasing it even further. Inaddition, electrical energy must be spent during the entire time tocontinuously make acceleration measurement.

In the case of gun-fired munitions, two other major problems areencountered with inertia-based sensors. Firstly, they must be made towithstand firing accelerations that in certain cases could be in excessof 100,000 Gs. However, to achieve the required guidance and controlaccuracy over relatively long distances and related times, the absoluteangular orientation of the projectile must be known during the entiretime of the flight within very small angles corresponding tosub-fractions of one G. Accelerometer also suffer from settling timeproblem after being subjected to the initial high G shock loading, whichfurther reduces their overall sensory precision. As a result, thedevelopment of high precision inertia based accelerometers and gyrosthat could withstand the aforementioned high G levels and require nearzero settling time is an extremely difficult task.

The second class of angular orientation sensors operates using opticalmethods. Such sensory systems can directly measure angular position ofone object relative to another. However, optical based angular positionsensory systems suffer from several disadvantages, including operationonly in the line of sight between two objects; accurate measurement ofrelative angular orientation only if the objects are relatively close toeach other; limited range of angular orientation measurement; relativelyhigh power requirement for operation; requirement of relatively cleanenvironment to operate; and in military applications the possibility ofexposing the site to the enemy. Optical gyros do not have most of theabove shortcomings but are relatively large, require a considerableamount of power, and are difficult to harden for high G firingaccelerations. Optical methods such as tracking of projectiles withsurface mounted reflectors and the like have also been developed, whichare extremely cumbersome to use even during verification testing, sufferfrom most aforementioned shortcomings, and are impractical for fieldedmunitions. In addition, the information about the object orientation canusually be determined only at the ground station and must be transmittedback to the moving object for guidance and control purposes. Thus,optical angular position sensors are generally not suitable formunitions and majority of other applications.

The third class of angular orientation sensors is magnetometers that canbe used to measure orientation relative to the magnetic field of theearth. The main problem with magnetometers is that they cannot measureorientation of the object about the magnetic field of the earth. Otherimportant issues are low sensitivity; requirement of an accurate map ofthe magnetic field of the area of operation; and sensitivity to thepresence of vehicles and the like in the area, the configuration ofwhich usually varies in time, particularly in an active war theatre.

The fourth class of angular orientation measurement systems are based onthe use of radio frequency (RF) antennas printed or placed on thesurface of an object to reflect RF energy emanating from a ground-basedradar system. The reflected energy is then used to track the object onthe way to its destination. With two moving objects, the radar measuresthe time difference between the return signals from each of the objectsand thereby determines angular information in terms of the angle thatthe relative velocity vector makes with respect to a coordinate systemfixed to one of the objects. With such systems, measurement of fullspatial orientation of an object (relative to the fixed radar or asecond object) is very difficult. In addition, the information about theobject orientation is determined at the radar station and must betransmitted back to the moving object(s) if it is to be used for coursecorrection. It is also very difficult and costly to develop systems thatcould track multiple projectiles. It is noted that numerous variationsof the above method and devices have been devised with all sufferingfrom similar shortcomings.

In addition to the above angular orientation measurement sensors, GPSsignals have also been used to provide angular orientation information.Such systems, however, have several significant shortcomings,particularly for munitions applications. GPS also provides mainly onlythe direction of travel in the plane of horizon. These include the factthat GPS signals may not be available along the full path of the flight;such orientation sensory systems are generally not very accurate; andthe measurements cannot be made fast enough to make them suitable forguidance and control purposes in gun fired munitions and mortars. Inaddition, GPS signals are generally weak and prone to jamming.

The fifth class of angular orientation sensors is based on utilizingpolarized Radio Frequency (RF) reference sources and mechanical cavitiesas described in U. S. Pat. Nos. 6,724,341 and 7,193,556, each of whichare incorporated herein by reference, and hereinafter are referred to as“polarized RF angular orientation sensors”. These angular orientationsensors use highly directional mechanical cavities that are verysensitive to the orientation of the sensor relative to the referencesource due to the cross-polarization and due to the geometry of thecavity. The reference source may be fixed on the ground or may beanother mobile platform (object). Being based on RF carrier signals, thesensors provide a longer range of operation. The sensors can also workin and out of line of sight. In addition, the sensors make angularorientation measurements directly and would therefore not accumulatemeasurement error. The sensor cavities receive the electromagneticenergy emitted by one or more polarized RF sources. The angular positionof the cavity sensor relative to the reference source is indicated bythe energy level that it receives. A system equipped with multiple suchwaveguides can then be used to form a full spatial orientation sensor.In addition, by providing more than one reference source, full spatialposition of the munitions can also be measured onboard the munitions.

The polarized RF based angular orientation sensors provide highlyprecise angular orientation measurements. The sensors, when embedded ina mobile platform such as in a projectile, can measure full angularorientation of the projectile (mobile platform) relative to the fixedground station or another moving object such as a UAV or anotherprojectile (mobile platform) where the reference source is located.These angular orientation sensors are autonomous, i.e., they do notacquire sensory information through communication with a ground,airborne or the like source. The sensors are relatively small and can bereadily embedded into the structure of most mobile platforms includingmunitions without affecting their structural integrity. Thus, suchsensors are inherently shock, vibration and high G accelerationhardened. A considerable volume is thereby saved for use for other gearand added payload. In addition, the sensors become capable ofwithstanding environmental conditions such as moisture, water, heat andthe like, even the harsh environment experienced by munitions duringfiring. In addition, the sensors require a minimal amount of onboardpower to operate since they do not have to be continuously operating andmay be used only when the sensory information is needed.

The above class of RF based full angular orientation sensors aredependent on the magnitude of the received signal at the cavity sensorsfrom the reference source to determine the orientation of the sensorrelative to the reference source. This is the case, for example, for theangular orientation sensors which are based on utilizing polarizedcavity sensors described in U.S. Pat. Nos. 6,724,341 and 7,193,556.

Briefly, referring now to FIGS. 1 and 2, there is shown a representationof a cavity sensor 100 and its operation with respect to a polarizedradio frequency (RF) reference (illuminating) source 101. Anelectromagnetic wave consists of orthogonal electric (E) and magnetic(H) fields. The electric field E and the magnetic field H of theilluminating beam are mutually orthogonal to the direction ofpropagation of the illumination beam. When polarized, the planes of Eand H fields are fixed and stay unchanged in the direction ofpropagation. Thus, the illuminating source establishes a (reference)coordinate system with known and fixed orientation. The cavity sensor100 reacts in a predictable manner to a polarized illumination beam.When three or more cavity sensors are distributed over the body of anobject, and when the object is positioned at a known distance from theilluminating source, the amplitudes of the signals received by thecavity sensor 100 can be used to determine the orientation of the objectrelative to the reference (illuminating) source 101, i.e., in theaforementioned reference coordinate system of the reference source 101.The requirement for the proper distribution of the cavity sensors 100over the body of the object is that at least three of the cavity sensorsbe neither parallel nor co-planar.

It is therefore observed that the aforementioned classes of RF basedfull angular orientation sensors are dependent on the magnitude of thereceived signal at the cavity sensors from the reference source todetermine the orientation of the sensor relative to the referencesource. The use of the signal magnitude, however, has several majorshortcomings that limits the utility of such sensors as well as degradestheir angular orientation measurement precision. The following are themajor shortcomings of the use of signal magnitude information in thesecavity sensors for measuring angular orientation relative to thepolarized RF reference sources:

-   -   1. To relate the magnitude of the received signal to angular        orientation, the distance from the reference source to the        angular orientation sensors must be known. This in general means        that other means must be also provided to measure or indicate        the position of the orientation sensors relative to the        reference source.    -   2. In practice, the signal received at the angular orientation        sensor would be noisy, it may face losses due to the        environmental conditions, and is also prone to measurement        errors at the sensor.    -   3. The magnitude of the signal received at the angular        orientation sensors and its relationship to the angular        orientation of the sensors (object to which the sensors are        attached) could be significantly different when the object is        not in the line-of-sight of the reference source. Therefore,        when the object is not in the line-of-sight, the received signal        magnitude information cannot yield an accurate angular        orientation measurements.

SUMMARY

The use of polarized RF reference sources with scanning capability wouldeliminate the above shortcomings of polarized RF cavity angularorientation sensors. This would be the case since scanning provides themeans of transmitting scanning patterns that are detected by the cavitysensors, from which the sensor angular orientation information can beextracted due to the sensitivity of the received signal to theorientation of the cavity sensor relative to the scanning referencesource. In addition, since the cavity sensor is used to detect thepattern of the received signal and not its magnitude and since thesignal pattern does not change with distance (only the magnitude of thepattern is reduced by distance), therefore the angular orientationmeasurement becomes independent of the distance between the referencesource and the cavity sensor. Another advantage of using polarized RFscanning reference sources is that in non-line-of-sight conditions,since obstacles do not affect the direction of the plane of polarizationand only reduce the signal strength, therefore the signal pattern andthe angular orientation information is not affected. Another advantageof using polarized RF scanning reference sources is that since noise andeffects of reflections and multi-paths for low wavelength (highfrequency) RF transmitted signals is random, their net effect canreadily eliminated by proper signal pattern detecting processing.

The method of constructing a polarized RF scanning reference source andits operation are described in detail in U.S. Pat. Nos. 8,164,745;8,259,292; 8,446,577 and 8,514,383, each of which are incorporatedherein by reference. In short, referring to FIG. 3, by modulating theamplitudes of the synchronized and polarized fields E_(x) and E_(y), thereferencing source transmits a scanning polarized vector field Ē(t). Byproperly modulating the two field amplitudes, the desired vector fieldscanning pattern is obtained. It is noted that E_(x) and E_(y) do nothave to be orthogonal.

In general, any desired scanning pattern may be implemented with thepresent polarized RF scanning reference source. For example, one maychoose scanning patterns with peaks that are sharper than a simpleharmonic sine wave, thereby increasing the accuracy of a peak detectionalgorithm. Alternatively, one may add specially designed patterns thatwill simplify a pattern detection algorithm being used and/or to rejectnoise, and/or to reduce their susceptibility to detection and jamming,or for other application specific purposes.

It is noted that the following method may also be used to provide two oreven more simultaneous and arbitrarily oriented scanning referencesources. Such multi-range scanning is useful for the establishment of anetwork of reference sources and/or to limit the range or radiation whenmultiple sensors (for example, munitions and/or weapon platforms) areusing the reference source.

In general, the signal received by cavity sensors from a polarized RFreference source will be sensitive to changes in orientation about anyaxis (for example the axes indicated by θ_(x), θ_(y) and θ_(z) in FIG.2). The cavity sensors may, however, be designed with geometries thatwhen positioned in certain direction relative to the referencing sourcethey would be more sensitive to change in one orientation and lesssensitive to others. For example the cavity sensor 100 shown in theschematic of FIG. 2 may be designed to be highly sensitive to roll(rotation about the axis Y_(ref)- or the so-called roll), and lesssensitive to rotations about the axes X_(ref) and Z_(ref), i.e., havehigh sensitivity to roll and low cross-sensitivity to pitch and yaw.

A need, however, exists for methods to design cavity sensors that areconstructed to measure roll angle (i.e., rotation of the cavity sensor100 about the Y_(ref) of the reference source 101), or yaw angle (i.e.,rotation of the cavity sensor 100 about the Z_(ref) of the referencesource 101, which is the direction of the transmitted electromagneticwave), or pitch angle (i.e., rotation of the cavity sensor 100 about theX_(ref) of the reference source 101).

A need also exists for methods to design cavity sensors that areconstructed to measure roll, yaw and pitch angles in the referencecoordinate system of a polarized RF scanning reference source with thepolarized vector field Ē(t) scanning as shown in FIG. 3, with the wavetraveling in the direction perpendicular to the E_(x) and E_(y) planefrom the reference source.

A need also exists for methods to synthesize efficient polarized RFreference source scanning patterns that can provide the informationrequired for angle measurement calculations at the cavity sensor and forthe method of calculating the angle at the sensor cavity, i.e.,processing the received signal at the sensor cavity to extract anglemeasurement.

An objective is to provide methods to design cavity sensors for roll,yaw and pitch angles measurement in the reference coordinate system of apolarized RF scanning reference source with the polarized vector fieldĒ(t) scanning as shown in FIG. 3, with the wave traveling in thedirection perpendicular to the E_(x) and E_(y) plane from the referencesource.

Another objective is to provide methods to synthesize efficientpolarized RF reference source scanning patterns that can provide theinformation required for angle measurement calculations at the cavitysensor and methods of calculating the angle at the sensor cavity, i.e.,processing the received signal at the sensor cavity to extract anglemeasurement.

In addition, several methods and related systems have been developed forproviding the sensory information for remotely guiding an object to adesired stationary or moving object or location. Such methods andrelated systems include those that use lasers that are pointed in thedesired direction or at a desired stationary or moving target object orlocation. Such methods and related system have a number of shortcoming,including limited range; that they work only in line-of-sight; and thatthey do not provide sensory information related to orientation about thedirection of travel, such as roll angle of a remotely guided flyingobject, for example, an Unmanned Aerial Vehicle (UAV) or a rocket. Othermethods include the use of radar and visual observation, both of whichmethod have the shortcoming of requiring communication with the flyingobject from a base (control) station to transmit the positioninformation or command corrective action. For this reason, neithermethod can provide the guidance sensory information more one or at mosta few flying objects. Visual observation does generally work duringnight or bad weather and non-line-of-sight and has very short range.Radar does not provide object orientation information and is notsuitable for relatively small and non-metallic objects. Other methodsalso include the use of GPS, which may not be available at the locationand/or may not be accurate enough for a given application and/or mayhave been jammed or spoofed. The GPS signal also does not provide objectangular orientation information. Other methods also include inertialnavigation sensors which are prone to drift over time and in which thetarget information must be provided at the start of the flight and canbe varied only through a communication link. Other shortcomings ofinertial sensors were previously indicated.

It is appreciated by those skilled in the art that a methods and systemsto function as “homing” sensors for guiding flying objects remotely to adesired location or to intercept a moving target, where the desiredlocation or to moving target to be intercepted is designated from afixed or mobile station can also be used for guiding mobile objects,such as Unmanned Ground Vehicles (UGV) or the like on the ground orunmanned moving objects on water or serve as a “homing” sensor to directthe driver of a manned ground vehicles or the like towards the saiddesired location or to intercept a moving target.

Hereinafter, the methods and sensory devices and systems will bedescribed for a flying object with no intention of excluding theirapplication to fixed or mobile objects on the ground such as UGVs andother mobile platforms or even people or animals.

A need therefore also exists for methods and systems to function as“homing” sensors for guiding flying objects remotely to a desiredlocation or to intercept a moving target, where the desired location orto moving target to be intercepted is designated from a fixed or mobilestation.

A need also exists for methods and systems to function as “homing”sensors for guiding flying objects remotely to a desired location or tointercept a moving target, where the methods and systems can provideangular orientation information, preferably full angular orientationinformation, onboard the flying object.

In many applications, there is also a need that the said methods andsystems to function as “homing” sensors for guiding flying objectsremotely to a desired location or to intercept a moving target berelatively low power and occupy relatively small volumes. This isparticularly desirable in munitions, UAVs and the like applications.

Another objective is to provide methods and systems that would functionas “homing” sensors for guiding flying objects remotely to a desiredlocation or to intercept a moving target, where the desired location orto moving target to be intercepted is designated from a fixed or mobilestation.

Another objective is to provide methods and systems that would functionas “homing” sensors for guiding flying objects remotely to a desiredlocation or to intercept a moving target, where the methods and systemscan provide angular orientation information, preferably full angularorientation information, onboard the flying object.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the apparatus ofthe present invention will become better understood with regard to thefollowing description, appended claims, and accompanying drawings where:

FIGS. 1 and 2 illustrate a schematic representation of a cavity sensorwith respect to a polarized radio frequency (RF) reference source of theprior art.

FIG. 3 illustrates a scanning polarized vector field Ē(t) of a polarizedRF scanning reference source that is generated by two synchronized andorthogonally directed modulating polarized RF transmitters that arepositioned at the origin of the Cartesian XY coordinate system O.

FIG. 4 illustrates the configuration of a polarized RF scanningreference source and a cavity sensor for measuring roll angle.

FIG. 5 illustrates the scanning polarized vector field Ē(t) obtained bymodulating the amplitudes of the synchronized and polarized fields E_(x)and E_(y) and the indicated roll angle as shown in the configuration ofFIG. 4.

FIG. 6 is the plot of an example of the transmitted polarized fieldsE_(x) and E_(y) for the pattern for roll angle measurement.

FIG. 7 is the plot of the detected signal pattern (top) for thetransmitted polarized fields E_(x) and E_(y) of FIG. 6 and its ω, 2ω and3ω harmonic amplitudes (bottom).

FIG. 8 illustrates the roll, pitch and yaw angles of an object asmeasured in the coordinate system of the polarized RF scanning referencesource.

FIG. 9 illustrates the method of reflecting a polarized RF scanningelectromagnetic wave by the provided metallic surface positioned at 45degrees angle against the incoming wave for the measurement of an objectyaw angle.

FIG. 10 illustrates the frontal view of an example of a cavity sensorthat is designed for yaw angle measurement.

FIG. 11 illustrates cross-sectional view B-B of the cavity sensor ofFIG. 10, which is designed for yaw angle measurement.

FIG. 12 illustrates the method of reflecting a polarized RF scanningelectromagnetic wave by the provided metallic surface positioned at 45degrees angle against the incoming wave for the measurement of an objectpitch angle.

FIG. 13 illustrates the polarized RF scanning reference source and apair of identical cavity sensors configured as roll and yaw anglemisalignment sensory system of a “homing” sensory system.

FIG. 14 illustrates the polarized RF scanning reference source with thepair of cavity sensors of FIG. 13, with the added two identical cavitysensors configured as roll and pitch angle misalignment sensory systemof a “homing” sensory system.

FIG. 15 illustrates an example of the design of an integrated pair ofdifferential angular orientation misalignment measuring cavity sensor.

FIG. 16 illustrates the cross-sectional view C-C of the integrated pairof differential angular orientation misalignment measuring cavity sensorof FIG. 15.

FIG. 17 illustrates an example of the design of a two pair integrateddifferential full angular orientation misalignment measuring cavitysensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The roll, pitch and yaw angle sensory systems is best described as beingconfigured for measuring the roll angle of an object to which the sensorcavity is provided, as shown in FIG. 4. FIG. 4 shows a polarized RFscanning reference source 200 to which the XYZ Cartesian coordinatesystem is fixed. In the coordinate system XYZ, the Z axis is along thedirection of the propagating electromagnetic wave d (in the −Z directionusing the right hand rule). A cavity sensor 202 is fixed to an object204 and is positioned a distance din far field of the polarized RFscanning reference source, attached to the object. The roll angle θ ofthe cavity sensor 202 (i.e., of the object 204) is measured from thesensor cavity orientation shown in FIG. 4, such that at the roll angleθ=0 and with polarized fields E_(x) being transmitted while thepolarized field E_(y) is off, the cavity sensor output is maximum. Thisroll angle referencing configuration is arbitrary and may be varied butis selected since it simplifies the roll angle measurement calculationsdescribed below. In addition, for a symmetrically designed sensor cavity202 like the horn shaped cavity sensor 100 of FIG. 1, the roll angle θ=0configuration corresponds to the orientation in which cross-polarizationangle of the transmitted polarized field E_(x) with the receiving cavitysensor terminal is also zero.

Referring to FIG. 5, by modulating the amplitudes of the synchronizedand polarized fields E_(x) and E_(y), the referencing source transmits ascanning polarized vector field Ē(t). By properly modulating the twofield amplitudes, the desired vector field scanning pattern is obtained.It is noted that E_(x) and E_(y) do not have to be orthogonal. In thepresent configuration of FIG. 4, the (roll) angle to be measured by thesensor is the angle θ as shown in FIGS. 4 and 5.

FIG. 5 shows the scanning polarized vector field Ē(t) obtained bymodulation of the amplitudes of the synchronized and polarized fieldsE_(x) and E_(y) (traveling in the XZ and YZ planes, respectively) of thepolarized RF scanning reference source and the aforementioned roll angleθ. As was previously described, by properly modulating the amplitudes ofthe two fields E_(x)and E_(y), the desired vector field scanning patternis obtained. It is noted that E_(x) and E_(y) do not have to beorthogonal.

The field strength detected by the cavity sensor 202 at an angle θ isgiven by the scalar function R(t) as

R(t)=g (d) f ( E (t), θ)   (1)

where g(d) is the gain related to the distance d between the scanningreference source and the cavity sensor and the existing environmentalfactors. Since the time taken to make an angle measurement is verysmall, changes in the gain g (d) during each angle measurement arenegligible and the gain g(d) can be considered to stay constant.

The mapping function f (Ē, θ) is determined by the design of the cavitysensor and its calibration. The geometry of the cavity is designed andthe pick-up terminal are located to maximize sensitivity to roll angleand minimize sensitivity to pitch and yaw. Since the angle θ is measuredby matching the scanning pattern, the effect of the fixed gain g(d) iseliminated during each angle measurement as described in the followingexample pattern.

For a properly formulated scanning pattern for the polarized RFreference source, the roll angle θ is readily extracted from thereceived signal at the cavity sensor from the measured amplitude patternof the vector R(t), the known mapping function f (Ē, θ), and thescanning pattern of the vector Ē(t) as shown in the following example.

As an example, consider a scanning vector field Ē(t)=E_(x)(t)î+E_(y)(t)ĵformed by the orthogonal synchronized polarized electric field signalsE_(x)(t) and E_(y) (t) shown in FIGS. 4 and 5, and which are modulatedas follows

E _(x)(t)=α (cos ωt+cos 2ωt)   (2)

E _(y)(t)=α (sin ωt+sin 3ωt)+b   (3)

where ω is the fundamental frequency of both signals, α is a constantsignal amplitude and b is the constant that provides a proper amplitudemodulation index.

The electric field detected by the cavity sensor 202 will then become

$\begin{matrix}\begin{matrix}{{R(t)} =} & {{g(d)}( {{{E_{x}(t)}\mspace{14mu}\cos\;\theta} + {{E_{y}(t)}\mspace{14mu}\sin\;\theta}} )} \\{=} & {{g(d)}\{ {{\lbrack {{a( {{\cos\;\omega\; t} + {\cos\; 2\omega\; t}} )} + b} \rbrack\cos\;\theta} +} } \\ &  {\lbrack {{a( {{\sin\mspace{14mu}\omega\; t} + {\sin\; 3\omega\; t}} )} + b} \rbrack\sin\;\theta} \} \\{=} & {{g(d)}\lbrack {{a\mspace{14mu}( {{\cos\;\omega\; t\mspace{14mu}\cos\;\theta} + {\sin\;\omega\; t\mspace{14mu}\sin\;\theta}} )} +} } \\ &  {{a\;\cos\;\theta\;\cos\; 2\omega\; t} + {a\;\sin\;\theta\;\sin\; 3\omega\; t} + {b( {{\sin\;\theta} + {\cos\;\theta}} )}} \rbrack \\{=} & {{g(d)}\lbrack {{a\mspace{14mu}{\cos( {{\omega\; t} - \theta} )}} + {a\;\cos\;\theta\;\cos\; 2\omega\; t} +} } \\ &  {{a\;\sin\;\theta\;\sin\; 3\omega\; t} + {b( {{\sin\;\theta} + {\cos\;\theta}} )}} \rbrack\end{matrix} & (4)\end{matrix}$

It is readily seen from (4) that the roll angle θ can be determined fromthe phase shifting of the fundamental frequency ω and the zero crossingof the fundamental frequency occurs when the harmonics 2ω and 3ω are inphase. As expected, the gain g(d) does not affect the angle measurement,therefore angle measurement has become independent of position(distance) measurement.

The polarized RF scanning pattern of equations (2) and (3) is shown tohave the unique characteristic of yielding the roll angle and timereference through readily detectable fundamental frequency and its firsttwo harmonics. The detection electronics is also made simple and lowcost and since the pattern is known to the detection signal processingunit, the roll angle can be recovered even when the signal-to-noiseratio of the measured RF signal is very low and even below unity. Infact, a signal pattern may even be hidden in the environmental noise,making the system immune to all countermeasures. The polarized nature ofthe scanning pattern along with being transmitted in short and randompulses, makes it almost impossible to jam or spoof.

In addition, high angular precision is possible due to the complexmodulation patterns, and mapping of the angular space to the timedomain. With off-the-shelf components, time measurement accuracy hasbeen shown to be better than 0.1%. Thus, angle accuracy, which isproportional to time, can become better than 0.06° for a scan range of+/−30°.

It will be appreciated by those skilled in the art that otherinformation is also available in the transmitted signal pattern and thereceived signal that can be used to increase the precision androbustness of the angle measurement. For example, the amplitude of thefundamental frequency can provide distance information.

In addition, the ratio of the amplitudes of the second and firstharmonics, i.e., the ratio of the amplitudes of the harmonics withfrequencies 3ω and 2ω, respectively, is seen to be tan(θ), whichprovides a second measurement for the roll angle. As a result, the anglemeasurement can be made more accurately and the sensory system becomesmore robust. In addition, by using more harmonics of the fundamentalfrequency, the angle measurement can be made from multiple phase shiftsand multiple ratios of the amplitudes of the higher harmonics of thefundamental frequency, thereby significantly increasing the anglemeasurement accuracy and the robustness of the sensory system.

One very important feature of the patterns of the type presented in thisexample is that they provide a reference position angle, which is fixedin the referencing coordinate system of the scanning referencing source.In this case, the time zero of the scanning pattern occurs when the twoharmonics 2ω and 3ω are in phase, from which the phase shift in thefundamental frequency ω, i.e., the roll angle θ is determined.

As an example, in the orthogonal synchronized polarized electric fieldsignals E_(x)(t) and E_(y) (t) of equations (2) and (3), let a=1 andb=2. The resulting polarized electric field patterns E_(x)(t) andE_(x)(t) are shown in FIG. 6 for a period of the fundamental frequencyT.

The roll angle θ can then be measured from the detected signal and itsfundamental frequency and first two harmonics. As an example, theamplitude pattern of the detected signal (i.e., the magnitude of thevector R(t), equation (4)) and its fundamental frequency ω and its firsttwo harmonics 2ω and 3ω at the roll angle θ=30° are shown in FIG. 7, inwhich the fundamental frequency can be seen to have shifted π/12 of theperiod T, corresponding to the roll angle θ=30°. The time zero is whenthe harmonics 2ω and 3ω are in phase, i.e., at time T/4.

The cavity sensors 202 are geometrical cavities with one or more pick upterminals that are designed to provide output that varies withorientation of the sensor with respect to the direction of the incomingpolarized RF plane of polarization. The cavities are designed for highsensitivity to the desired orientation variation and for relatively lowcross-sensitivity. In general, the geometry of the cavities is designedthrough an iterative process of trial and errors using Finite Element(FE) modeling and Finite Element Analysis (FEA) software for modelingsensor structures and determining their interaction with the incoming RFwaves.

For a cavity sensor 202 that is designed with certain sensitivity to theangle θ but has linear characteristic to the amplitude of Ē, the mappingfunction f (Ē, θ) can be expressed as

f ( E , θ)=| E |f′(θ-< E )   (5)

Then the electric field detected by this cavity becomes

$\begin{matrix}\begin{matrix}{{R(t)} =} & {{g(d)}\lbrack {{{E_{x}(t)}\mspace{14mu}{f^{\prime}(\theta)}} + {{E_{y}(t)}\mspace{14mu}{f^{\prime}( {\theta - \frac{\pi}{2}} )}}} \rbrack} \\{=} & {{g(d)}\{ {{\lbrack {{a( {{\cos\;\omega\; t} + {\cos\; 2\omega\; t}} )} + b} \rbrack{f^{\prime}(\theta)}} +} } \\ &  {\lbrack {{a( {{\sin\mspace{14mu}\omega\; t} + {\sin\; 3\omega\; t}} )} + b} \rbrack{f^{\prime}( {\theta - \frac{\pi}{2}} )}} \} \\{=} & {{g(d)}\lbrack {{a( {{\cos\;\omega\; t\mspace{14mu}{f^{\prime}( {\theta - \frac{\pi}{2}} )}} + {\sin\;\omega\; t\mspace{14mu}{f^{\prime}(\theta)}}} )} +} } \\ & {{{{af}^{\prime}( {\theta - \frac{\pi}{2}} )}\cos\; 2\omega\; t} + {{{af}^{\prime}(\theta)}\sin\; 3\omega\; t} +} \\ &  {b( {{f^{\prime}(\theta)} + {f^{\prime}( {\theta - \frac{\pi}{2}} )}} )} \rbrack \\{=} & {{g(d)}\lbrack {{a\sqrt{{f^{\prime}( {\theta - \frac{\pi}{2}} )}^{2} + {f^{\prime}(\theta)}^{2}}{\cos( {{\omega\; t} - \phi} )}} +} } \\ & {{{{af}^{\prime}( {\theta - \frac{\pi}{2}} )}\cos\; 2\omega\; t} + {{{af}^{\prime}(\theta)}\sin\; 3\omega\; t} +} \\ &  {b( {{f^{\prime}(\theta)} + {f^{\prime}( {\theta - \frac{\pi}{2}} )}} )} \rbrack\end{matrix} & (6)\end{matrix}$

where

$\phi = {\tan^{- 1}{\frac{f^{\prime}(\theta)}{f^{\prime}( {\theta - \frac{\pi}{2}} )}.}}$

The angle θ can then be determined from the phase shift ϕ. Similaramplitude relationships define the amplitudes of the frequencies 2ω and3ω, and the time zero of the scanning pattern still occurs when the twoharmonics 2ω and 3ω are in phase.

The roll, pitch and yaw angles as measured in the Cartesian coordinatesystem XYZ of the polarized RF scanning reference source 200 are shownin FIG. 8. As can be seen in FIG. 8, the yaw angle is measured about anaxis on the object 204 that is parallel to the reference source Y axis,which is perpendicular to the direction of wave travel. Thus, byproviding a cavity sensor 204 with a metallic reflecting surface 206 at45 degrees angle in the path of propagating wave as shown in FIG. 9(reflecting the propagating wave 90 degrees about the x axis as shown inFIG. 9), thereby causing the synchronized and polarized vector fieldsE_(x) and E_(y) to be transformed to polarized vector fields E′₁and E′₂,respectively, and the scanning vector field Ē is transformed to scanningvector field Ē′, which indicates the measured yaw angle as shown in FIG.9.

A cavity sensor 300 designed for roll and yaw angle measurement is shownin the frontal view of FIGS. 10. The cross-sectional view B-B of thecavity sensor of FIG. 10 is shown in FIG. 11, with the direction of wavepropagation from the reference source shown by the indicated arrow. Thereflecting surface 206 and the roll angle probe 302 and yaw angle probe304 are shown in FIG. 11, as well as a pitch angle probe 306. The cavitysensor 300 of FIGS. 10 and 11 was designed through an optimizationprocess for high sensitivity to yaw and minimal cross-sensitivity topitch angle of +/−5 degrees. For yaw angle measurement, the roll angleis measured independently and used together with the roll angle measuredin this sensor to eliminate the effect of roll angle cross-sensitivityon the yaw angle measurement. The optimal cavity sensor was obtainedusing a parametric FE model of the cavity geometry and the propagatedpolarized RF incoming wave using ANSYS, Inc. software with addeddeveloped routines.

It is appreciated by those skilled in the art that as the cavity sensor300 shown in FIGS. 10 and 11 rotates in pitch as indicated in FIG. 8, ascan be seen in FIG. 9, scanning vector filed Ē′ will rotate about theaxis which will be picked up the pitch angle probe 306 shown in FIG. 11.For pitch angle measurement, the roll and yaw angles are measuredindependently and used together with the roll and yaw angles measured inthis sensor to eliminate the effect of roll and yaw anglecross-sensitivity on the pitch angle measurement.

In another embodiment, the pitch angle is measured using the same methodas the aforementioned method for yaw angle measurement, i.e., byproviding a metallic reflective surface 206 at 45 degrees angle in thepath of the propagating wave to reflect the wave as shown in FIG. 12(reflecting the propagating wave 90 degrees about the y axis as shown inFIG. 9), thereby causing the synchronized and polarized vector fieldsE_(x) and E_(y) to be transformed to the polarized vector fields E′_(x)and E′_(y), respectively, and the scanning vector field Ē is transformedto scanning vector filed Ē′, which indicates the measured yaw angle Φ asshown in FIG. 12.

The cavity sensor 300 for pitch angle measurement can have a designsimilar to that of FIGS. 10 and 11 for yaw angle measurement, exceptthat the cavity sensor is to be rotated 90 degrees about the directionof wave propagation shown by the arrow in FIG. 11. As a result, theindicated yaw angle sensor 304 would now measure the pitch angle.

The polarized RF scanning reference source 200 and properly configuredsensor cavities can be configured function as “homing” sensors forguiding flying objects remotely to a desired location or to intercept amoving target, where the desired location or to moving target to beintercepted is designated from a fixed or mobile station.

Here, the different methods and sensory system embodiments will bedescribed using sensor cavities used for roll angle measurement, but itwill be appreciated by those skilled in the art that sensor cavitiesdesigned for pitch and/or yaw or any combination of cavity sensorsdesigned for roll, pitch and yaw angle measurement may also be similarlyconfigured to function as the “homing” sensors.

A method for the construction the “homing” sensory system embodimentsconsists of configuring the previously described cavity sensors asdifferential roll, pitch or yaw angle misalignment sensors for detectingangular misalignment of the object in the coordinate system of thepolarized RF scanning reference source 200 (roll, and/or pitch and/oryaw misalignment with zero roll, and/or pitch and/or yaw, respectively,FIG. 8), as well as lateral and/or up and down (as seen in the schematicof FIG. 8) translational deviation (of the sensor cavities of theobject—as is described below) from the YZ and/or XZ planes of thepolarized RF scanning reference source, FIG. 8.

Consider the polarized RF angular orientation sensory system for rollangle measurement shown in the schematic of FIG. 4. Let the polarized RFscanning reference source 200 be fixed while the cavity sensors 202 arefixed to the flying object 204, directly facing the polarized RFscanning reference source 200 as shown in FIG. 4. In addition, insteadof a single cavity sensor 202 shown on the rolling object 204 of FIG. 4,two identical cavity sensors, indicated as the cavity sensor “A” 202Aand cavity sensor “B” 202B, are positioned symmetrically on the surfaceof the flying object facing the polarized RF scanning reference source200 on the boom as shown in FIG. 13.

The cavity sensors “A” 202A and “B” 202B shown in FIG. 13 are “horn”shaped and geometrically designed for maximum sensitivity to roll anglerelative to the incoming scanning plane of polarization (the roll anglesensitivity being due to cross-polarization as well as the internalgeometry of the sensor cavity). As can be seen in FIG. 13, the sensorcavities “A” 202A and “B” 202B are also slightly tilted inwards as shownby the dotted lines. Thus, the cavity sensors also have asymmetricsensitivity to rotation about the Y-axis, FIG. 4, relative to thepolarized RF scanning reference source (yaw angle when the x-axis of theobject and the X-axis of the polarized RF scanning reference source areparallel, FIGS. 4 and 13).

Now let the polarized RF scanning pattern of the reference source 200 besymmetric about the Y-axis of the reference source. Thus, thedifferential measurement of the signal received at the cavity sensorpair 202A, 202B will be zero only when the roll angle as well as the yawangle of the object 204 relative to the polarized RF scanning referencesource 200, FIGS. 4 and 13. Therefore, the differential output of thecavity sensor pair 202A, 202B will be zero only if the X-axis of thepolarized RF scanning reference source 200, FIG. 4, is parallel with thex-axis of the object 204, FIG. 14, and the plane Y-Z of the polarized RFscanning reference source 200, FIG. 4, and the object fixed y-z plane,FIG. 13, are parallel, i.e., when the object 204 has zero roll and yawangles relative to the reference source but may have a pitch anglerelative to the reference source 200. The distance between the Y-Z andy-z planes may also be non-zero. It is noted that in FIGS. 4 and 13 theaxes Z and z are not shown for the sake of illustration clarity, but arereadily identifiable for the Cartesian coordinate systems XYZ of thepolarized RF scanning reference source and xyz of the object using theright-hand rule.

Now if we add a second similar pair of identical cavity sensors “C” 202Cand “D” 202D to the object 204 of FIG. 13 and position themsymmetrically about the x-axis as shown in FIG. 14 with dashed lines,the differential output of the second pair of cavity sensors 202C, 202Dto a polarized RF scanning pattern of the reference source 200 that issymmetric about the X-axis of the polarized RF scanning reference source200 becomes zero only if the roll angle as well as the pitch angle ofthe object 204 relative to the reference source 200 are zero as wassimilarly described for the differential output of the cavity sensors“A” 202A and “B” 202B.

Therefore, the differential output of the second cavity sensor pair “C”and “D” 202C and 202D will be zero only if the Y-axis of the polarizedRF scanning reference source 200, FIG. 4, is parallel with the y-axis ofthe object 204, FIG. 14, and the X-Z and x-z planes are in parallel,i.e., the object has zero roll and pitch angles relative to thepolarized RF scanning reference source 200, but may have a yaw anglerelative to the reference source 200. The distance between the parallelX-Z and x-z planes may also be non-zero.

It will be appreciated by those skilled in the art that with thedescribed design of the polarized RF scanning reference source 200, itis possible to sequentially scan each sensor cavity pair 202A, 202B and202C, 202D with scanning patterns that are symmetric about their axes ofsymmetry. Therefore, the sensory system can provide the desired measureof angular misalignment between the polarized RF scanning referencesource 200, FIG. 4, and the object 204, FIG. 14, with a single polarizedRF scanning reference source 200.

The differential signal measurement from the above two cavity sensorpairs 202A, 202B and 202C, 202D provides a measure of pitch, yaw androll misalignment between the polarized RF scanning reference source 200and the object 204. Hereinafter, the system consisting of the polarizedRF scanning reference source 200, FIG. 4, and the two pairs of identicalcavity sensors 202A, 202B and 202C, 202D, FIG. 14, that are configuredto measure pitch, yaw and roll misalignments is referred to as “angularmisalignment sensory system”. It is appreciated by those skilled in theart that this system may be used with only one pair of cavity sensors“A” 202A and “B” 202B or the pair “C” 202C and “D” 202D to only measureangular misalignment in roll and yaw or roll and pitch, respectively.

In the schematic of FIG. 14 the pair of identical cavity sensors “A”202A and “B” 202B and the pair of identical cavity sensors “C” 202C and“D” 202D are shown to be identical. However, it will be appreciated bythose skilled in the art that the two pairs do not have to be identicalas long as they are oriented symmetrically about the YZ and XZ planes,respectively, they can provide the above angular misalignment measures.

When the object 204 is provided with an active control system that isused for its guidance towards a fixed location or a moving target, thecontrol system can use the differential measurements as error signals tobe minimized to align the object to zero roll, yaw and pitch anglerelative to the Cartesian coordinate system XYZ of the polarized RFscanning reference source 200, FIG. 4.

It will also be appreciated by those skilled in the art that thestrength of the signal received at each cavity sensor of the abovecavity sensor pairs, i.e., the signal strength at any one of the fourcavity sensors “A” 202A, “B” 202B, “C” 202C and “D” 202D provides ameasure of the distance between the polarized RF scanning referencesource 200 and the object 204. Then when the object 204 is provided withan active control system that is used for its guidance towards a fixedlocation or a moving target, the control system can use theaforementioned “angular misalignment sensory system” and the measure ofdistance (as a distance error) to be minimized (negative value of themagnitude of the indicated measure of distance to increase and drive theobject 204 towards the fixed or moving target and away from thepolarized RF scanning reference source 200—or positive value of themagnitude of the indicated measure of distance to decrease the distancebetween the object 204 and the polarized RF scanning reference source200).

It will also be appreciated by those skilled in the art that instead ofusing the magnitude of the signal at only one of the cavity sensors “A”202A, “B” 202B, “C” 202C or “D” 202D, a better measure of distance isgenerally an average of the magnitudes of the signals measured at leastat two of the cavity sensors since it would minimize variations due toinevitable angular motions of the object 204 during the flight (such aswobbling in munitions during the flight) or ground motion.

It will also be appreciated by those skilled in the art that when the“angular misalignment sensory system” and the aforementioned distancemeasure are used for bringing the object 204 as shown in FIGS. 4 and 14towards the polarized RF scanning reference source 200, e.g., for thepurpose of mating two parts or bringing a UAV or UGV “home”, since thedistance between the cavity sensors 202 and the polarized RF scanningreference source 200 at their intended and final relative positioning isknown, and since the magnitudes of the signal at all four cavity sensorsat the final relative positioning are known a priori, an accuratemeasurement of distance between the object 204 and the polarized RFscanning reference source 200 can be readily calculated. In practice,however, one would only require a measure of distance between the object204 and the reference source 200 and its rate of change (rate ofdecrease in the distance) to close a control loop—manually orautomatically—to achieve guidance of the object 204 to its intendedrelative positioning (“homing” or “engaging” or “mating” positions,depending of the nature of the object and the receptacle on thereference source side). In addition, auxiliary sensors indicating fullengagement, such as optical sensors or mechanical mating guides, etc.,may also be provided depending on the application to ensure properengagement and for safety reasons.

In the description of the pairs of identical sensor cavities of FIGS. 13and 14 the cavity sensors were shown to be located at the same radialdistance from the origin of the provided coordinate system. In practice,however, each pair may be located at a different radial distance fromthe origin of the coordinate system fixed on the object 204 as were aslong as they are symmetrically positioned to indicate zero roll anglewith a symmetrically scanning reference pattern.

In the above descriptions of the “angular misalignment sensory system”with and without the distance measure for guidance control of the objecttowards the desired location or towards a fixed or moving object, thepolarized RF scanning reference source 200 was considered to be fixed.However, the polarized RF scanning reference source 200 may be mobile,for example, being held by the “target designator” and used to manuallyorient the polarized RF scanning reference source 200 to guide theobject 204 in the direction of target intercept. During this process,the “target designator” can readily “command” the object 204 to make aturn a certain amount, e.g., to the right, by rotating the polarized RFscanning reference source 200 the same amount to the right(counterclockwise about the Y-axis, FIG. 8, if the object 204 istraveling in a plane parallel to the XZ plane).

In one embodiment, the “target designator” is a human and is carryingthe polarized RF scanning reference source 200, preferably as mounted ona support such as a tri-pod with a ball joint to allow its rotarymotions for directional stability, in which the “target designator”views the object 204 and the target with or without optical aids, anddirects the object 204 (equipped for operating with the present “angularmisalignment sensory system” and provided with active guidance andcontrol) towards the target by proper rotation of the polarized RFscanning reference source 200.

In another embodiment, the polarized RF scanning reference source 200 isprovided with rotary actuators that are controlled by a central controlsystem, hereinafter indicated as the “target intercept controller”. Inthis system, the “target designator” indicates the target through avision system. The vision system directly or through the targetdesignator also identifies the location of the guided object 204, anduses the information to generate a control signal for orienting thepolarized RF scanning reference source 200 in an established closed loopcontrol system in the “target intercept controller” to intercept thefixed or moving target.

In the above embodiments, the polarized RF scanning reference source 200is essentially fixed and the object 204 is in motion (in flight ormoving on the ground or on water), FIGS. 4 and 8. In an alternativeembodiment, the object 204 is mounted on a fixed or mobile platform byan orientationally actuated mechanism that is operated by a controllersystem, which forms an “angular misalignment sensory system” with aremotely positioned polarized RF scanning reference source 200. Theoperator of the polarized RF scanning reference source can then manuallyor automatically remotely orient the object 204 in the desireddirection. Here, the operator is not intended to refer only to a humanoperator but it might also consist of an automated targetacquisition/recognition system, such as one that uses radar or a visualtarget pattern recognition system or the like.

Alternatively, in an “angular misalignment sensory system” bothindicated polarized RF scanning reference source 200 component and theobject 204 component, FIGS. 4 and 8, may be mobile and the signalgenerated by the “angular misalignment sensory system” is used tomanually or automatically bring the two components 200, 204 to a desiredrelative positioning (“homing”), such as to mate the two components orplace one inside the other or the like. In this embodiment, thepreviously described distance measure (the magnitude of the signalmeasured at any one of the cavity sensors “A” 202A, “B” 202B, “C” 202Cor “D” 202D or their average or the like and the corresponding known(calibrated) magnitude(s) of the sensor signal at the desired relativepositioning of the two components 200, 204 of the “angular misalignmentsensory system”. Here, it will be appreciated that the relativepositioning of the two components 200, 204 of the “angular misalignmentsensory system” refers to both their relative distance and orientationpositioning.

In the schematics of FIGS. 13 and 14 the pairs of symmetricallypositioned identical cavity sensors are shown to be constructed with twoseparate cavity sensor sides 404. Each pair may, however, be constructedas a single cavity with a single pick-up terminal as shown in FIG. 15and its cross-sectional view C-C shown in FIG. 16. Such a design of anintegrated pair of differential angular orientation misalignmentmeasuring cavity sensor 400 would significantly simplifying the sensorconstruction and its required electronics. FIG. 15 shows the frontalview of the integrated sensor pair as it would have been viewed in thefrontal views of FIG. 13 or 14. The cross-sectional view C-C of theintegrated sensor is shown in FIG. 15, also showing the location of thesensor pick-up probe 402. Alternatively, two pick-up probes, eachsymmetrically positioned in each cavity as shown in FIG. 11 for rollangle measurement may be provided to provide signal magnitudemeasurement in each cavity to provide a measure of distance between theobject and the polarized RF scanning reference source as was previouslydescribed. The differential measurement of the signal provides a measureof angular misalignment as was previously described.

It will be appreciated by those skilled in the art that numeroussymmetrical cavity sensor geometries can also be designed to provide thedifferential sensory information of the cavity sensor pairs of FIGS. 13and 14. In fact, both pairs of cavity sensors of FIG. 14 can be combinedinto a single geometrical cavity with one or two pick-up probes (notshown) for full roll, pitch and yaw angle misalignment measurement. Anexample of such a combined cavity sensor 450 is shown in frontal view ofFIG. 17. This cavity sensor 450 is constructed as a simple integrationof two cavity sensors of the geometry shown in FIG. 15, one of which isrotated 90 degrees and symmetrically positioned as shown in FIG. 17. Thefour cavity sides 404 are combined as shown in the cross-section of FIG.16 and the pick-up probe 402 of the sensor is positioned at 45 degreesas shown in FIG. 17 inside the cavity sensor base similar to that shownin FIG. 16. As a result, the differential reading from both integratedpairs of cavity sensors have to be zero for the object to be at zeropitch, yaw and roll angles relative to the polarized RF scanningreference source, FIG. 8. Separate pick-up terminal can be provided formagnitude (distance) indication. Other pick-up terminals similar tothose shown in the cavity sensor of FIG. 11 for roll angle measurementmay also be provided to make the angular orientation measurements as waspreviously described. The use of one pick-up probe may, however, not bedesirable since it must be positioned to be sensitive to both pairs ofdifferential cavity sensors, thereby requiring a higher transmittedpower level for the same sensor output.

It will appreciated by those skilled in the art that when the disclosedroll angular orientation cavity sensor of FIG. 9-11 is used in aspinning object such as a spinning munitions, only one such sensorcavity is generally required to measure both yaw and pitch angles sinceas the object rotates from the position of measuring the yaw angle 90degrees, the cavity sensor indicates the object pitch angle.

In a spinning object, such as a spinning round, the differential rollangle sensor cavity pairs like the one shown in FIG. 11 have zero outputeach time the roll angle is either zero or 180 degrees. As a result, bymeasuring the time that it takes for the differential measurements to gothrough zero outputs the spin rate of the round can be determined.

While there has been shown and described what is considered to bepreferred embodiments of the invention, it will, of course, beunderstood that various modifications and changes in form or detailcould readily be made without departing from the spirit of theinvention. It is therefore intended that the invention be not limited tothe exact forms described and illustrated, but should be constructed tocover all modifications that may fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for determining angular orientation ofan object in two or more directions, the method comprising: generating ascanning polarized RF source signal; receiving the scanning polarized RFsource signal at one or more cavities of a sensor disposed on theobject; measuring the scanning polarized RF source signal at a firstportion of the sensor; reflecting the scanning polarized RF sourcesignal toward a second portion of the sensor; measuring the scanningpolarized RF source signal at the second portion of the sensor; anddetermining the angular orientation of the object in the two or moredirections based on the measured signal at the first and second portionsof the sensor.
 2. The method of claim 1, wherein the determiningdetermines the angular orientation of the object in the threedirections.
 3. The method of claim 2, wherein the three directions areroll, pitch and yaw angles.
 4. The method of claim 3, wherein thescanning polarized RF source signal is generated by a polarized RFscanning reference source and the roll, pitch and way angle aredetermined relative to a position of the polarized RF scanning referencesource.
 5. The method of claim 1, wherein the first portion of thesensor is an open end of the one or more cavities of the sensor and thesecond portion of the sensor is at a closed end of the one or morecavities of the sensor.
 6. The method of claim 1, wherein the reflectingcomprises reflecting the scanning polarized RF source signal at an angleof 45degrees toward the second portion of the sensor.